Six-coordinate molybdenum nitrosyls with a single ene-1,2-dithiolate ligand

Article abstract of DOI:10.1016/S0020-1693(02)01127-1

The synthesis and molecular structures of the (Tp*)Mo(NO)(S-S) family of compounds (where (Tp*) is hydrotris(3,5-dimethyl-1-pyrazolyl)borate; (S-S) is an ene-1,2-dithiolate) are reported. The compounds; (Tp*)Mo(NO)(bdt) (1), (Tp*)Mo(NO)(tdt) (2), and (Tp*)Mo(NO)(bdtCl₂) (3) (bdt, 1,2-benzenedithiolate; tdt, 3,4-toluenedithiolate; bdtCl₂, 3,6-dichlorobenzenedithiolate), are the first such structurally characterized {MoNO}⁴ compounds that contain a [(Tp*)Mo(NO)]²⁺ fragment ligated to an ene-1,2-dithiolate. The compounds crystallize in the space groups P2₁/c (1) (a=11.115(2) ?, b=13.667(3) ?, c=16.410(3) ?; β=98.36(3), Volume=2466.4(8) ?³, Z=4); P2₁/n (2) (a=15.579(3) ?, b=9.942(2) ?, c=16.527(3) ?; β=95.79(3), Volume=2546.7(9) ?³, Z=4); and Pnma (3) (a=17.9879(9) ?, b=13.2277(7) ?, c=11.2505(6) ?; Volume=2676.9(2) ?³, Z=4). The molecular structures show that the inner coordination sphere remains invariant within this family. A remarkable feature is the fold angle (0) between the MoS₂ plane and S₂C₂ plane of the ene-1, 2-dithiolate chelate ring. The fold angles (0) of 42.1 in 1, 41.1 in 2 and 44.4 in 3 are substantially larger than in analogous compounds with a terminal oxo group. Additional insight into the chemistry and properties of complexes 1-3 has been obtained by cyclic voltammetry, IR, NMR, electronic absorption and He I photoelectron (PES) spectroscopies.

Full text of DOI:10.1016/S0020-1693(02)01127-1

Inorganica Chimica Acta 337 (2002) 275ꢂ286
/
www.elsevier.com/locate/ica
Six-coordinate molybdenum nitrosyls with a single ene-1,2-dithiolate
ligand
Hemant K. Joshi, Frank E. Inscore, Julien T. Schirlin, Ish K. Dhawan, Michael
D. Carducci, Tonja G. Bill, John H. Enemark *
Department of Chemistry, University of Arizona, Tucson, AZ 85721, USA
Received 8 March 2002; accepted 11 June 2002
This paper is dedicated to Professor Karl Wieghardt.
Abstract
The synthesis and molecular structures of the (Tp*)Mo(NO)(Sꢀ
/
S) family of compounds (where (Tp*) is hydrotris(3,5-dimethyl-1-
pyrazolyl)borate; (SꢀS) is an ene-1,2-dithiolate) are reported. The compounds; (Tp*)Mo(NO)(bdt) (1), (Tp*)Mo(NO)(tdt) (2), and
/
(Tp*)Mo(NO)(bdtCl2) (3) (bdt, 1,2-benzenedithiolate; tdt, 3,4-toluenedithiolate; bdtCl2, 3,6-dichlorobenzenedithiolate), are the first
such structurally characterized {MoNO}4 compounds that contain a [(Tp*)Mo(NO)]2ꢀ fragment ligated to an ene-1,2-dithiolate.
˚
˚
˚
The compounds crystallize in the space groups P21/c (1) (aꢁ
/
11.115(2) A, bꢁ
/
13.667(3) A, cꢁ
/
16.410(3) A; bꢁ
/
98.36(3)8,
3
3
2546.7(9) A ,
˚
˚
˚
˚
˚
Volumeꢁ
/
2466.4(8) A , Zꢁ
/
4); P21/n (2) (aꢁ
17.9879(9) A, bꢁ
/
15.579(3) A, bꢁ
/
9.942(2) A, cꢁ
/
16.527(3) A; bꢁ
/
95.79(3)8, Volumeꢁ
/
3
˚
˚
˚
˚
Zꢁ4); and Pnma (3) (aꢁ
/
/
/
13.2277(7) A, cꢁ
/
11.2505(6) A; Volumeꢁ
/
2676.9(2) A , Zꢁ4). The molecular
/
structures show that the inner coordination sphere remains invariant within this family. A remarkable feature is the fold angle (u)
between the MoS2 plane and S2C2 plane of the ene-1, 2-dithiolate chelate ring. The fold angles (u) of 42.18 in 1, 41.18 in 2 and 44.48
in 3 are substantially larger than in analogous compounds with a terminal oxo group. Additional insight into the chemistry and
properties of complexes 1ꢂ
/
3 has been obtained by cyclic voltammetry, IR, NMR, electronic absorption and He I photoelectron
(PES) spectroscopies.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Molybdenum nitrosyls; Ene-1,2-dithiolate; Fold angle; Photoelectron spectroscopy
1. Introduction
Mononuclear metalꢂ
which, in principle, could allow the design of a high
capacity storage device [11].
The transition metalꢂnitrosyl complexes reveal a
/nitrosyl complexes are of con-
/
tinuing interest [1,2]. Their possible applications include;
molecular sensors [3], magnetically-dilute hosts for
paramagnetic guests [4], non-linear optical [5] and
significant mixing between the metal d and p* (NO)
orbitals which led to the development of the {MNO}n
formalism for describing mononitrosyl complexes
[12,13]. In this notation n is the total number of
electrons contained in the metal d and p* (NO) orbitals.
The title complexes are six-coordinated {MNO}4 spe-
cies, with the metal center coordinated to a bulky
tripodal ligand (Tp*). The steric interaction of (Tp*)
prevents additional coordination to the metal center,
hence, affording stable six-coordinate 16-electron spe-
cies, which have a formally 4d4 electronic configuration
(i.e. Mo(II)). The {MNO}4 center in (Tp*)Mo(NO)Cl2
can be reduced by one electron to the corresponding
paramagnetic {MNO}5 center, and EPR spectroscopy is
ferrimagnetic materials [6,7]. Metalꢂnitrosyls are biolo-
/
gically relevant as they are implicated in the immune
system to kill tumor cells [8], as a physiological NO
carrier [9], and as intracellular parasites [10]. The
metastable linkage isomers of transition metal nitrosyl
complexes have potential technological importance
* Corresponding author. Tel.: ꢀ
8407
E-mail address: jenemark@u.arizona.edu (J.H. Enemark).
/
1-520-621-2245; fax: ꢀ1-520-521-
/
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 1 1 2 7 - 1

276
H.K. Joshi et al. / Inorganica Chimica Acta 337 (2002) 275ꢂ286
/
consistent with the unpaired electron being localized in a
MO that is predominantly Mo 4dxy [3,14,15]. McClev-
erty and Jones and their coworkers have prepared a
series of homo and heterobimetallic complexes in which
the redox active (Tp*)Mo(NO)(X, Y) (where X, Y are
mono anions) center is linked to a second redox active
metal center through polyene bridges [16,17]. These
binuclear systems with a reducible {MNO}4 center are
of general interest due to their possible application as
non-linear optical materials.
The synthesis of compound 2 was first reported by
McCleverty and coworkers in 1989 [19]. However, this
family of compounds has remained essentially unex-
plored in the intervening years as evident by a recent
review of the coordination and organometallic chemis-
try of metalꢂ
/
NO complexes [1]. Complexes 1ꢂ/3 (Fig. 1)
are the first structurally characterized Moꢂ
/
nitrosyl
complexes containing a single ene-1,2-dithiolate (S2C2)
chelate. However, it has long been known that the
h5-
crystal structures of LMo(NO)(SC6H5)2 (where Lꢁ
/
Numerous metal nitrosyl complexes have been struc-
turally characterized. A Cambridge Crystallographic
C5H5, Tp*(8)) exhibit unusual ONꢀMoꢀSꢀC torsion
/
/
/
angles Fig. 2(A) that have been ascribed to dp-pp
bonding interactions between the thiolate lone pairs,
primarily S 3p in character, and the empty Mo 4dxy
orbitals [20,21]. Molecular orbital calculations by Hoff-
mann and coworkers suggested that the sulfur atoms
can contribute to the stability of 16-electron systems
[22,23]. Fourmigue´ et al. have shown that the fold angle
u, Fig. 2(B) is sensitive to the electronic occupation of
Database (CSD) search showed 2037 hits of metalꢂ
nitrosyl structures, out of which 542 hits were of Group
VI transition metalꢂnitrosyl complexes and 292 hits had
/
/
molybdenum centers [18]. A total of ten structures
containing mononuclear 16-electron [(Tp*)Mo(NO)-
(S,S)] cores (where (S,S)ꢁtwo sulfur donor ligands)
/
including the title complexes, are structurally compared
here (Chart 1).
metalꢂ
the ene-1,2-dithiolate chelate in compounds 1ꢂ
have a d0xy ground state, exhibit a large fold angle (u).
Similar to (Tp*)Mo(NO)Cl2, the metal centers in 1ꢂ
can be reduced by one electron to yield the spectro-
scopically interesting d1xy state (formally (dxzdyz)4d1xy
/
dithiolate complexes [24,25]. Here we show that
/3, which
Chart 1. Classification, n(NO) (IR, KBr), and Ab-
breviations of (Tp*)Mo(NO)(S,S) Compounds ((Tp*):
hydrotris(3,5-dimethyl-1-pyrazolyl)borate).
/
3
)
(S,S)
Compound n(NO) References
[14] whose detailed study will be presented elsewhere
[29].
number
(cmꢃ1
1670
1660
)
bdt
tdt
1
2
This work
[19], this
work
Compounds 1ꢂ3 are of further interest because the
/
active sites of sulfite oxidase and xanthine oxidase have
a molybdenum atom coordinated by a single ene-1,2-
bdtCl2
3
4
5
6
7
8
9
10
1674
1667
1653
1644
1634
1682
1672
1662
This work
[54]
[46]
[46]
[55]
[21,50]
[51]
[51]
dithiolate at the active site [27,28,30ꢂ
/32]. This
S(CH2)2CONH(CH2)2S
(1,4-(SCH2)2C6H4)2
(1,4-(SCH2)2C6H4)3
(Fe(h5-C5H4S)2)
(SC6H5)2
pyranopterinꢂdithiolate unit coordinated to molybde-
/
num is postulated to function as an electron transfer
conduit and modulator of the redox potential of the
enzyme active site [33]. The electronic structure of these
active sites and their relationship to electron transfer is
(SCH2CONHCH3)2
(SC2H4CONHCH3)2
not yet understood; however, the metalꢂsulfur interac-
/
tion appears to play an important role [34]. The inner
coordination-sphere of the small molecular models of
the active site seems invariant, even though large
differences are observed in the reduction potentials
(bdt) 1,2-benzenedithiolate, (tdt) 3,4-toluenedithio-
late, (bdtCl2) 3,6-dichlorobenzenedithiolate.
[35ꢂ37]. It has been suggested that modulation of the
/
Fig. 1. Representation of the [(Tp*)Mo(NO)]2ꢀ system containing
Fig. 2. (A: left and B: right): Orbital interaction diagram in
(Tp*)Mo(NO)(SPh)2 and (Tp*)Mo(NO)(SꢀS) complexes.
equatorial ene-1,2-dithiolate ligands (Sꢀ
/
S) coordinated to the Mo
S) are also shown.
/
center. Structures of the dithiolate dianions (Sꢀ
/

H.K. Joshi et al. / Inorganica Chimica Acta 337 (2002) 275ꢂ
/
286
277
fold angle (u) might be pivotal in tuning the properties
of these active sites and their models [35,36].
were acquired on a Bruker DRX-500 spectrometer
1
operating at a H frequency of 500.13 MHz using a 5
mm Nalorac triple-resonance 3-axis gradient probe.
Chemical shifts were referenced to residual CHCl3 at
7.24 ppm.
2. Experimental
2.1. General
2.2. Synthesis of (Tp*)Mo(NO)(bdt) (1)
All reactions and manipulations were carried out
under an inert environment of argon gas using standard
Schlenk techniques, a high-vacuum/gas double line
setup, and an inert atmosphere glove bag. The argon
was predried by passing the high-purity-grade gas
through a series of drying towers. All glassware was
dried in an oven at 150 8C and Schlenk ware was
further purged by repeated evacuation and inert gas
flushes prior to use. Tetrahydrofuran (THF) and
In a 100 ml round bottom evacuated Schlenk flask,
C6H5CH3 (0.38 g, 0.5
mmol) was added to H2bdt (0.1 g, 0.7 mmol) in 50 ml of
dry, degassed toluene in a 100 ml round bottom Schlenk
flask for synthesis of 1. The mixture was deoxygenated
thoroughly with argon saturation while being stirred at
highly purified (Tp*)Mo(NO)I2×
/
ꢀ80 8C. Dry, degassed Et3N (0.4 ml, 2.2 mmol) was
/
added slowly dropwise via a gas tight syringe to this
rigorously stirring solution. The solution changed color
to greenish and later to deep blue. The reaction mixture
was refluxed for 16 h, and the reaction progress was
monitored by IR spectroscopy (shift of n(NO) stretching
frequency) and TLC analysis (disappearance of
(Tp*)MoV(NO)I2 precursor). Upon completion of the
toluene were distilled from Naꢂ
amine was distilled from Naꢂ
/
benzophenone; triethyl-
K amalgam [38]. The
/
prepurified solvents were subsequently transferred and
stored under N2 over fresh drying agents. These solvents
were freshly distilled under nitrogen prior to use,
thoroughly degassed by repeated freezeꢂ
/
thawꢂ/pump
reaction, the blueꢂ
/
green precipitate, primarily Et3Nꢄ
/
cycles, and transferred to reaction vessels via steel
cannulae under a positive pressure of inert gas. Dichlor-
omethane, 1,2-dichloroethane (DCE), cyclohexane, tol-
uene (EM Science, Omnisolv), n-hexane and n-pentane
(Burdick and Jackson) were used as received and
deoxygenated by bubbling with argon. Molybdenum
hexacarbonyl (Mo(CO)6, Aldrich) was dried in vacuum
prior to use. Potassium hydrotris(3,5-dimethyl-1-pyra-
zolyl)borate (KTp*), the precursor complexes
HI resulting from the proton abstraction and ligand
exchange processes, was removed by filtration from the
hot solution under dry argon. The filtrate was cooled to
r.t. and evaporated to dryness with a rotorary evapora-
tor. The solid dark-purple residue was re-dissolved in
toluene, concentrated under vacuum, and layered with
n-pentane. The dark-purple powder precipitate was
collected by filtration and washed with n-pentane until
the filtrate was clear. The powder was then dissolved in
dichloromethane, filtered to remove any insoluble
materials, and evaporated to dryness in vacuum. The
solid was pumped on for several hours to assure dryness
and the complete removal of excess triethylamine. The
solid material was re-dissolved in dichloromethane,
concentrated, and loaded on a silica gel chromato-
graphic column under a positive pressure of argon. A
dark-purple fraction (band 1) eluted off the column
using dichloromethane:cyclohexane (1:3) as the eluant.
Band 1 was further purified by a second silica gel
column using dichloromethane:cyclohexane (1:1) as the
eluant. The purity of compound was confirmed by TLC
analysis. The dark-purple solution, which was deemed
pure by TLC was evaporated to dryness in vacuum, re-
dissolved in dichloromethane, and layered with n-
pentane to yield a dark-purple crystalline material.
This material was filtered, washed with pentane and
then dried in vacuum. The product was characterized by
(Tp*)MoV(NO)(CO)2 and (Tp*)MoV(NO)I2×
/
C6H5CH3
and the ligands H2bdt (1,2-benzenedithiol) were pre-
pared according to literature procedures [26,39,40]. The
ligand
H2bdtCl2 (3,6-dichloro-1,2-benzenedithiol) employed in
S) compounds
H2tdt
(4-methyl-1,2-benzenedithiol)
and
the syntheses of the (Tp*)MoV(NO)(Sꢀ
/
(2, 3) were used as received from Aldrich.
TLC analysis was carried out on silica gel 60 F254
plastic sheets (EM Science) and column chromatogra-
phy was carried out in glass columns with silica gel
˚
(Merck, grade 9385, 230ꢂ400 mesh, pore diameter 60 A)
/
as the stationary phase. Mass spectra were recorded on a
JEOL HX110 high-resolution sector instrument utilizing
fast atom bombardment (FAB) ionization in a matrix of
3-nitrobenzyl alcohol (NBA). IR spectra (4000ꢃ400
/
cmꢃ1) were collected on a Nicolet Avatar ESP 360 FT
IR spectrophotometer in KBr disks or as dichloro-
methane solutions (between NaCl plates) at room
temperature (r.t.). Electronic absorption spectra of
samples dissolved in 1,2-dichloroethane solutions were
recorded with a 1 cm pathlength Helma quartz cell
IR, UVꢂVis and mass spectroscopy. Slow vapor diffu-
/
sion of n-pentane into a saturated dichloromethane
solution of 1 afforded diffraction quality crystals.
equipped with a teflon stopper, on a Cary 300 (250ꢂ
/
900
nm) spectrophotometer. Solvent background correc-
Characterization: HRMS [Mꢀ
/
H]ꢀ peak gives m/zꢁ
565.0798 (calculated, 565.0792) and corresponds to the
/
1
tions were made in all cases. H NMR (CDCl3) spectra
formula [12C21H27N711B32S325O98Mo], IR data (KBr)

278
H.K. Joshi et al. / Inorganica Chimica Acta 337 (2002) 275ꢂ286
/
n(Bꢀ
/
H)ꢁ
/
2551 cmꢃ1, n(NO) 1670 cmꢃ1, UVꢂ
(Mꢃ1 cmꢃ1)):732(13 700; 1576),
579(17 300; 4527), 370(27 000; 3154), 326(30 700; 3645),
/
Vis data
determinations are given in Table 1. The structures were
determined by direct methods and refined on F2 by full-
matrix least-squares with anisotropic parameters for the
non-hydrogen atoms. Scattering factors were taken
from Cromer and Waber [41], anomalous dispersion
effects were included for all non-hydrogen atoms with
the values of Df? and Dfƒ taken from Cromer [42], and
the structure was solved by direct methods using SHELXS
in the Bruker SHELXTL (Version 5.0) software package.
Hydrogen atoms were placed in calculated positions
with isotropic displacement parameters.
l(nm)(E(cmꢃ1));
ꢁ
/
292(34 200; 5898).1H NMR (500 MHz, CD2Cl2, 298 K):
3
d (ppm) 8.057, 7.274 (2H, dd, JHH
ꢁ4.5, 3.0 Hz; 2H,
/
3
dd, JHH
2.485, 2.404, 2.308 (7H, s; 4H, s; 7H, s).
ꢁ4.5, 3.0 Hz), 5.992, 5.623 (2H, s; 1H, s),
/
2.3. Synthesis of (Tp*)Mo(NO)(tdt) (2)
The preparation of (Tp*)MoNO(tdt) (2) followed
from published procedures [19].
A
mixture of
(Tp*)Mo(NO)I2×C6H5CH3 (0.9 g, 1.2 mmol) and
/
2.5.2. Crystal structure of 3
H2tdt (0.33 g, 2.1 mmol) were refluxed for 16 h instead
of 24 h as given in the literature [19]. Slight modifica-
tions were also made in the work up procedures to
obtain the pure compound suitable for growing X-ray
diffraction quality crystals. In our work-up procedure
the reaction mixture was evaporated to dryness under
reduced pressure and the solid obtained was dissolved in
a 1:3 CH2Cl2:cyclohexane mixture and subjected to
column chromatography. The product is contained in
a deep blue band that is well separated from other side
products, which do not separate well when eluted with
CH2Cl2 as in the original preparation [19]. Further
purification was achieved by a second column chroma-
tography step using 1:1 CH2Cl2:cyclohexane as the
eluant. Slow diffusion of heptane into a CH2Cl2 solution
of 2 yielded X-ray diffraction quality crystals. Com-
pound 2 reveals similar spectroscopic features to those
reported in the literature [19].
A dark-purple cuboid of 3 was mounted on a glass
fiber for structure determination using a Bruker
SMART 1000 CCD detector X-ray diffractometer.
Key parameters for the structure determination are
also summarized in Table 1. Empirical absorption and
decay corrections were applied using the program
SADABS. The structure was solved by direct methods
using SHELXS in the Bruker SHELXTL (Version 5.0)
software package. Refinements were performed on F2
by full-matrix least-squares with anisotropic displace-
ment parameters for all the non-hydrogen atoms (using
SHELXL and illustrations were made using XP). Hydro-
gen atoms were added at idealized positions, constrained
to ride on the atom to which they are bonded and given
thermal parameters equal to 1.2 or 1.5 times Uiso of that
bonded atom. Scattering factors and anomalous disper-
sion were taken from International tables Vol C, tables
4.2.6.8 and 6.1.1.4 [41,42].
2.4. Synthesis of (Tp*)Mo(NO)(bdtCl2) (3)
2.6. Photoelectron spectroscopy
All the synthetic steps were similar to those described
for 1, except for the stoichiometric ratio of the reagents.
He I gas-phase photoelectron spectra (PES) were
collected on an instrument with a 36 cm radius hemi-
spherical analyzer (8 cm gap, McPherson) and custom
designed sample cells, excitation sources, and detection
and control electronics [43,44]. The excitation source
was a quartz lamp with the ability to produce He I
photons (21.21 eV). The ionization energy scale for the
Highly purified (Tp*)Mo(NO)I2×/C6H5CH3 (677 mg,
1.00 mmol) was added to a solution of H2bdtCl2 (220
mg, 1.1 mmol) in 50 ml of dry, degassed toluene in a 100
ml round-bottom Schlenk flask. Characterization:
HRMS [Mꢀ
culated, 633.0002) and corresponds to the formula
[12C21H25N171B32S235Cl2O98Mo] for 3, IR (KBr) n(Bꢀ
H)ꢁn(BꢀH)ꢁ
2548 cmꢃ1; n(NO) 1674 cmꢃ1, UVꢂ
Vis data l(nm)(E(cmꢃ1); ꢁ (Mꢃ1 cmꢃ1)): 739(13 500;
/
H]ꢀ peak that gives m/zꢁ
633.0035 (cal-
/
2
He I experiments was calibrated by using the E1/2
/
ionization of methyl iodide (9.538 eV), with the argon
2P3/2 ionization (15.759 eV) used as an internal calibra-
tion lock during the experiment. During data collection
/
/
/
/
/
1583), 573(17 500; 6476), 372(26 900; 3734), 330(30 300;
1
5186), 294(34 000; 8477). H NMR (500 MHz, CD2Cl2,
the instrument resolution (measured using the FWHM
2
of the argon P3/2 ionization peak) was 0.022ꢂ
/0.025 eV.
298 K): d (ppm) 7.369 (1H, s), 6.017, 5.629 (2H, s; 1H,
s), 2.502, 2.415, 2.287 (7H, s; 4H, s; 7H, s).
All data were intensity corrected with an experimentally
determined instrument analyzer sensitivity function. The
He I spectra were corrected for the presence of ioniza-
tions from other lines (He Ib line, 1.9 eV higher in
energy and 3% the intensity of the He Ia line). All
samples sublimed cleanly with no detectable evidence of
decomposition products in the gas phase or as a solid
residue. The sublimation temperatures (in 8C, 10ꢃ4
2.5. X-ray crystal structure determinations
2.5.1. Crystal structures of 1 and 2
Crystals of 1 and 2 were mounted on glass fibers for
structure determination using an Enraf-Nonius CAD4
diffractometer. Crystal data and details of structure
Torr) were as follows: (Tp*)Mo(NO)(bdt), 209ꢂ2188;
/

H.K. Joshi et al. / Inorganica Chimica Acta 337 (2002) 275ꢂ
/
286
279
Table 1
Crystal data and structure refinement for complexes 1ꢂ
/
3
Identification code
1
2
3
Empirical formula
Formula weight
Temperature (K)
C21H26BMoN7OS2
563.36
298(2)
C22H28BMoN7OS2
577.38
298(2)
C21H24BCl2MoN7OS2
632.25
173(2)
˚
Wavelength (A)
0.71073
monoclinic
P21/c
0.71073
monoclinic
P21/n
0.71073
orthorhombic
Pnma
Crystal system
Space group
Unit cell dimensions
˚
a (A)
11.115(2)
13.667(3)
15.579(3)
9.942(2)
17.9879(9)
13.2277(7)
˚
b (A)
˚
c (A)
16.410(3)
90
16.527(3)
90
11.2505(6)
90
a (8)
b (8)
g (8)
98.36(3)
90
2466.4(8)
95.79(3)
90
2546.7(9)
90
90
3
˚
V (A )
Z
2676.9(2)
4
1.534
4
1.517
4
1.475
Dcalc (mg mꢃ3
)
Absorption coefficient (mmꢃ1
F(000)
)
0.729
11.52
0.729
1160
0.872
1252
Crystal size (mm3)
0.23ꢄ0.13ꢄ0.03
1.85 to 24.97
05h 513, 05k 516,
ꢃ1951 519
4328
0.17ꢄ0.12ꢄ0.08
1.71 to 24.97
05h 518, 05k 511,
ꢃ1951 519
4468
0.40ꢄ0.10ꢄ0.10
2.14 to 27.29
2u Range for utilized data (8)
Limiting indices
ꢃ235h 523, ꢃ165k 516,
ꢃ1451 51
26 517
Reflections utilized
Independent reflections
4328 [Rintꢁ0.0000]
100.0
None
4468 [Rintꢁ0.0000]
100.0
None
3004 [Rintꢁ0.0741]
95.5
Empirical
Completeness to uꢁ24.978 (%)
Absorption correction
Max/min transmission
Refinement method
0.9784, 0.8502
Full-matrix least-squares on F2
4328/0/289
0.9456, 0.8893
0.9179, 0.7219
Full-matrix least-squares on F2
3004/0/177
Full-matrix least-squares on F2
4468/0/314
1.051
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I ꢂ2s(I)]
R indices (all data)
1.043
1.069
R1ꢁ0.0630, wR2ꢁ0.1218
R1ꢁ0.1507, wR2ꢁ0.1454
0.855 and ꢃ0.550
R1ꢁ0.0484, wR2ꢁ0.1092
R1ꢁ0.0922, wR2ꢁ0.1222
0.631 and ꢃ0.327
R1ꢁ0.0517, wR2ꢁ0.1202
R1ꢁ0.0921, wR2ꢁ0.1457
0.595 and ꢃ0.521
Largest difference peak and
ꢃ3
˚
hole (e A
)
RMS difference density (e A
ꢃ3
˚
)
0.106
0.077
0.127
(Tp*)Mo(NO)(tdt), 220ꢂ
/
2298; (Tp*)Mo(NO)(bdtCl2),
218ꢂ2308.
/
3. Results and discussion
3.1. Synthesis and physical properties of
Tp*Mo(NO)(SꢀS) compounds
/
The identities of the reaction products were confirmed
by their high resolution mass spectra. The reaction
products 1ꢂ
oethane, toluene and benzene. Scheme 1 shows several
different routes to the synthesis of Tp*Mo(NO)(SꢀS)
complexes. The Tp*Mo(NO)X2 precursors (XꢁCl, Br,
/3 are soluble in dichloromethane, dichlor-
/
/
I) are well known; however, partial halogenation of the
pyrazole ring at C-4 position has been observed in the
preparation of Tp*Mo(NO)Cl2 and Tp*Mo(NO)Br2,
precursor [45]. In addition, use of the precursor
Tp*Mo(NO)Cl2 can lead to the formation of unexpected
Scheme 1. Synthetic routes to the (Tp*)Mo(NO)(S,S) compounds
[19,39,40,45,49].

280
H.K. Joshi et al. / Inorganica Chimica Acta 337 (2002) 275ꢂ286
/
products, including disulfide formation during the
synthesis of Tp*Mo(NO)((SCH2)2C6H4) [46]. The
3.2. Molecular structure analysis of (Tp*)Mo(NO)(Sꢀ
/
S) compounds
Tp*Mo(NO)I2×
used for the synthesis of Tp*Mo(NO)(Sꢀ
in this work because it is relatively easy to prepare from
Tp*Mo(NO)(CO)2 and the iodide ligand seems to be a
very good leaving group in the subsequent substitution
reactions [45].
/
C6H5CH3 precursor has been primarily
The structures of compounds 1ꢂ3, determined by
/
/S) complexes
single-crystal X-ray diffraction, are shown in Fig. 3.
Tables 2 and 3 show key geometric features of the
coordination environment of the Mo atom. Compounds
1ꢂ3 are the first structurally characterized six-coordi-
/
nate {MoNO}4 complexes that contain a single ene-1,2-
dithiolate ligand cis to the terminal nitrosyl group. We
have previously reported the structures and properties of
The solid-state IR spectra in KBr exhibited bands
characteristic of the (Tp*) ligand (n(Bꢀ
for 1, 2550 cmꢃ1 for 2 and 2548 cmꢃ1 for 3). This n(Bꢀ
H) is similar to that observed in the range of 2543ꢂ2549
cmꢃ1 for the related chelate complexes (including 5, 6)
[46]. The solution IR spectra of the (Tp*)Mo(NO)(SꢀS)
complexes in dichloromethane showed no significant
frequency shifts or additional bands, indicating that the
solid phase and solution structures are similar. The
purity of the products was also confirmed by the
absence of n(CO) and the shift in the n(NO) stretching
/
H)ꢁ
2551 cmꢃ1
/
/
the corresponding oxo analogues, (Tp*)MoO(Sꢀ
/S)
/
[4,35,52,53]. Compounds 1, 2 and 3 crystallize in three
different space groups P21/c, P21/n and Pnma. No
symmetry is imposed on 1 and 2 by their space groups,
but Cs symmetry is imposed on 3 by the space group
Pnma (Fig. 4). In the crystals of 3, the atoms N1, O1,
Mo1, B1, H1A, N31, N32, C33, C34, H34A, C35, C36,
H36A, C37, H37A lie on a mirror plane. In these
complexes the terminal nitrosyl ligand and the two
sulfur atoms of the ene-dithiolate are constrained to be
mutually cis to each other by the fac stereochemistry
imposed by the tridentate Tp* ligand. Thus molecules of
compounds 1 and 2 also have effective Cs symmetry. All
three molecules exhibit a distorted pseudo-octahedral
coordination geometry, in which the Mo atom is ligated
by a nitrogen atom from the nitrosyl ligand, two sulfur
/
vibrations
(Tp*)Mo(NO)(CO)2 (n(CO)ꢁ
1655 cmꢃ1
of
the
precursor
complexes
/
1906 cmꢃ1, n(NO)ꢁ
/
)
and (Tp*)Mo(NO)I2 (n(NO)ꢁ
/1700
cmꢃ1) which also served as a diagnostic tool for
monitoring the progress of the reaction.
The values of n(NO) range from 1674 for 3 to 1660
cmꢃ1 for 2 and decrease slightly with increasing electron
withdrawing properties of the substituents on the
benzene rings of the coordinated ene-dithiolates. The
donor atoms of the (Sꢀ/S) ligands and three nitrogen
donor atoms of the tridentate facially coordinated (Tp*)
ligand. The maximum angular deviations from ideal
octahedral geometry within the N2S2 planes of the
reduction potential (E1/2) of ꢃ
/
723 mV for 3, ꢃ
/
896 mV
for 2, and ꢃ862 mV for 1 also follows the trend 3ꢂ
/
/
1ꢂ
/
compounds are: 5.968 in 1 (N(21)ꢀ
in 2 (N(11)ꢀMo(1)ꢀS(1)) and 4.088 in 3 (N(21)ꢀ
S(2), N(11)ꢀMo(1)ꢀS(1)). The mean deviation of 4.008
/
Mo(1)ꢀ
/
S(2)); 5.528
2 [47]. McCleverty and coworkers have earlier proposed
a correlation between E1/2 and n(NO) [48]. Our results
also show that the more electron withdrawing the ene-
dithiolate the higher is the n(NO) stretch. Thus n(NO) is
a sensitive indicator of the perturbation of electron
density on the Mo center by the remote substitution on
the ene-dithiolate ligand.
/
/
/
Mo(1)ꢀ
/
/
/
in 1, 3.458 in 2 and 3.388 in 3 is consistent with
deviations observed in other structures based on
[(Tp*)Mo(NO)]2ꢀ fragment [21,46,50,51,54,55]. The
Nꢀ
/
Moꢀ
/
N angles between the nitrogen atoms of (Tp*)
The diamagnetic {MoNO}4 complexes have been
ligand are always less than 908.
Seven other structurally characterized complexes with
[(Tp*)Mo(NO)S2] cores are available in the CSD
database (Chart 1) [18]. Of these {MoNO}4 complexes,
1
probed using H NMR [1,19,39,40,45,49ꢂ
/
51]. The 1-D
NMR data and X-ray structures show that complexes
1ꢂ3 have effective Cs symmetry with two of the three
/
only 1ꢂ3 have five-membered ene-1,2-dithiolate chelate
/
1
pyrazolyl rings being magnetically equivalent. The H
NMR spectrum shows pyrazolyl methyl groups in the
(Tp*)-ligand as singlets of relative area 7:4:7 at d (ppm)
2.308, 2.404, 2.485 in 1 and d (ppm) 2.287, 2.415, 2.502
in 3. The pyrazolyl 4-H signals appeared as two signals
of relative area 1:2 at d (ppm) 5.623, 5.992 for 1 and d
(ppm) 5.629, 6.017 for 3. These are in the typical range
rings. The molecular structure of a complex containing
similar fragment and an oxygen containing five mem-
bered chelate ring (catechol) has been reported earlier, in
which boron sequestering resulted in the degradation of
the (Tp*) ligand skeleton [49]. Structurally characterized
chelate compounds 4, 5 and 6 contain nine, 17 and 25
membered chelate rings, respectively, [46,54]. Com-
pound 7 contains the organometallic chelate ligand
1,1?-dithiaferrocenyl-S,S? [55]. Compounds 8, 9 and 10
possess two mono thiolates [21,50,51].
of CH3 (d (ppm) 1.5ꢂ3.0) and pyrazolyl 4-H (d (ppm)
/
5.0ꢂ6.5) shifts for other (Tp*)Mo(NO)(S,S) complexes
/
[49]. The aryl protons of the bdt2ꢃ ligand in 1 resonate
as two doublets of doublets (4.5, 3.0 Hz) at d (ppm)
The structural parameters (bond lengths and angles)
for the [(Tp*)Mo(NO)]2ꢀ core reported in Table 2 for
compounds 1, 2 and 3 are similar to one another and
2ꢃ
7.274 and 8.057 and those protons of the bdtCl2
ligand in 3 resonate as one singlet at d (ppm) 7.369.

H.K. Joshi et al. / Inorganica Chimica Acta 337 (2002) 275ꢂ
/
286
281
Fig. 3. The ORTEP drawing of (Tp*)Mo(NO)(bdt) (1), (Tp*)Mo(NO)(tdt) (2), and (Tp*)Mo(NO)(bdtCl2) (3). The atoms are drawn as 50%
probability ellipsoids. H-atoms have been made arbitrarily small for clarity.
also agree with those found for compounds 4 through 10
˚
N1 distance of 1.818(6) A
properties of the nitrosyl ligand [3] is not as pronounced
as the trans effect in the corresponding oxo-Mo
analogue of complex 3 where the strong p-donor and
(Chart 1). The observed Moꢀ
/
˚
˚
in 1 is 0.044 A (8s) longer than that of 1.774 (6) A in
complexes 2 and 3. All three values are between the
s-donor properties of the oxo-ligand lengthen the
˚
largest (1.839 A in 7) and the smallest (1.730 A in 5).
˚
˚
corresponding Moꢀ
/
N31 distance (2.391(3) A) by 0.214
˚
˚ ˚
Another structural parameter of interest in metal
A relative to Moꢀ
to MoꢀN11 (2.166(3) A) [35].
The MoꢀS1 and MoꢀS2 distances are 2.374(2) A and
/
N21 (2.177(2) A) and 0.225 A relative
˚
nitrosyl complexes is the Mꢀ
174.2(6)8 in 1, 175.0(4)8 in 2 and 174.5(5)8 in 3. The
other MoꢀNꢀO angles in Chart 1 range from 179.0268
in 8 to 172.4318 in 7. A nearly linear MoꢀNꢀO unit is
expected for a six-coordinate {MoNO}4 compound [13].
/
Nꢀ/O angle. This angle is
/
˚
/
/
˚
˚
˚
2.3882(19) A in 1, 2.3773(15) A and 2.4078(15) A in 2
/
/
1
˚
and 2.3926(12) A in 3 . The average Moꢀ
/
S bond lengths
of 2.3811 A in 1 and 2.3926 A in 3 compares with 2.376
/
/
˚
˚
˚
and 2.374 A in the corresponding oxo-Mo anologues.
˚ ˚
O bond distance is 1.113(7) A in 1, 1.171(5) A in
The Nꢀ
/
˚
Thus a slight Moꢀ
/
S bond lengthening is observed in
2, and 1.181(7) A in 3, and shows no correlation with
n(NO).
nitrosylꢂMo family in the chelate complexes which is
/
opposite of the trend observed in non-chelated com-
plexes. A bond reduction is observed from an average
Additional structural features common in these com-
pounds are the angles between trans ligands. The angle
˚
˚
value of 2.382 A in (Tp*)MoO(SPh)2 to 2.357 A in
(Tp*)Mo(NO)(SPh)2 (8). It is interesting to note that the
involving the nitrosyl nitrogen atom (N1ꢀ
close to 1808, whereas other two trans angles (S1ꢀ
N21) fall in the range 160ꢂ
/
Moꢀ
/
N31) is
Moꢀ
1668.
/
/
N11 and S2ꢀ
/
Moꢀ
/
/
1
Compound 3 shows the strongest trans effect from a
terminal nitrosyl group of all of the compounds in Table
˚ ˚
The shortest Moꢀ
nitrosyl complexes containing at least two sulfur donor ligands
/
S distance in mononuclear group VI transition-
metalꢂ
/
˚
is 2.289 A in (tris(2-thioethyl)amine-N ,S ,S ?,S ƒ) ꢂ
/
nitrosyl ꢂ
molybdenum [56] and the longest is 2.639 A in (2,3:8,9-dibenzo-
1 , 4 , 7 , 1 0 - t e t r a t h i a d e c a n e - S , S ?, S ƒ, S ?ƒ) ꢂ n i t r o s y l ꢂ
diphenyl(methyl)phosphineiminatoꢂmolybdenum(III) [57].
/
2. Its Moꢀ
/
N31 distance (2.258(5) A) is 0.110 A longer
˚
˚
N21 (both 2.148 A). This
relative to Moꢀ
/
N11 and Moꢀ
/
/
/
trans effect due to the strong s-donor and p-acceptor
/
Table 2
˚
Comparison of key bond lengths and parameters for compounds with [(Tp*)Mo(NO)S2) core (all of the bond lengths and trans effects are in A and
angles in 8)
Compounds MoꢀN1 MoꢀN1ꢀO1 MoꢀN31 MoꢀN21 MoꢀN31 MoꢀS1
MoꢀS2
S1ꢀMoꢀS2 N1ꢀMoꢀX DT
8d
1
2
1.818(6) 174.2(6)
1.774(4) 175.0(4)
1.774(6) 174.5(5)
2.181(6)
2.187(4)
2.148(3)
2.230
2.164(5)
2.161(4)
2.148(3)
2.234
2.260(6)
2.257(4)
2.258(5)
2.249
2.374(2)
2.3882(19) 84.17(8)
86.14(10)
87.26(14)
87.63(13)
96.547
0.088 175.0
0.080 174.4
0.110 174.7
0.017 164.2
0.022 166.6
0.024 166.0
0.064 167.5
0.034 172.7
0.020 165.0
0.041 166.1
2.3773(15) 2.4078(15) 83.79(5)
2.3926(12} 2.3926(12) 83.96(6)
3
4
1.767
1.730
1.759
1.839
1.763
1.763
1.791
175.939
173.309
176.764
172.431
179.026
176.904
177.605
2.342
2.366
2.345
2.375
2.345
2,347
2.337
2.352
2.340
2.339
2.357
2.368
2.349
2.345
105.171
102.612
102.248
90.278
5
2.237
2.238
2.231
2.234
2.256
2.260
95.691
94.462
6
7
2.202
2.215
2.197
2.205
2,263
2.244
98.165
90.950
8
102.957
102.820
104.353
9
10
2.223
2.209
2.219
2.222
2.242
2.256
95.638
95.794
DTꢁtrans effect [(MnꢀN31)ꢃ(average MoꢀN11 and MoꢀN21)]. 8dꢁdihedral angle between planes MoꢀN11ꢀN21 and MoꢀSlꢀS2.

282
H.K. Joshi et al. / Inorganica Chimica Acta 337 (2002) 275ꢂ286
/
Table 3
˚
Selected bond lengths (A), bond angles (8) and torsion angles (8) (e.s.d.’s in parentheses)
1
2
3
N(1)ꢀO(1)
S(1)ꢀC(1)
S(2)ꢀC(2)
C(1)ꢀC(2)
1.113(7)
1.758(9)
1.726(8)
1.406(11)
1.171(5)
1.734(6)
1.751(6)
1.413(7)
1.181(7)
1.743(5)
1.743(5)
1.431(7)
N(1)ꢀMo(1)ꢀS(1)
N(1)ꢀMo(1)ꢀS(2)
N(1)ꢀMo(1)ꢀN(21)
N(1)ꢀMo(1)ꢀN(11)
N(21)ꢀMo(1)ꢀN(31)
N(21)ꢀMo(1)ꢀN(11)
N(21)ꢀMo(1)ꢀN(31)
N(21)ꢀMo(1)ꢀS(1)
N(21)ꢀMo(1)ꢀS(2)
N(11)ꢀMo(1)ꢀS(31)
N(11)ꢀMo(1)ꢀS(1)
N(11)ꢀMo(1)ꢀS(2)
N(31)ꢀMo(1)ꢀS(1)
N(31)ꢀMo(1)ꢀS(2)
C(1)ꢀC(2)ꢀS(2)
84.6(2)
87.67(18)
97.4(2)
87.78(14)
86.75(14)
95.06(18)
97.72(17)
177.38(17)
81.59(15)
84.27(16)
97.52(12)
177.80(12)
84.70(14)
174.48(11)
96.94(11)
89.79(11)
93.98(11)
121.2(4)
87.63(13)
87.63(13)
96.40(16)
96.40(16)
178.0(2)
97.6(2)
176.7(2)
81.3(2)
84.2(2)
82.17(19)
85.07(14)
96.80(10)
175.92(10)
96.80(10)
175.92(10)
96.80(10)
90.92(11)
90.92(11)
120.52(16)
120.52(16)
99.35(16)
174.04(16)
85.5(2)
177.65(16)
94.97(15)
92.32(15)
90.83(15)
120.1(6)
121.6(6)
C(2)ꢀC(1)ꢀS(1)
120.3(4)
N(1)ꢀMo(1)ꢀS(1)ꢀC(1)
N(1)ꢀMo(1)ꢀS(2)ꢀC(2)
N(21)ꢀMo(1)ꢀS(1)ꢀC(1)
N(21)ꢀMo(1)ꢀS(2)ꢀC(2)
N(21)ꢀMo(1)ꢀN(1)ꢀO(1)
N(11)ꢀMo(1)ꢀS(1)ꢀC(1)
N(11)ꢀMo(1)ꢀS(2)ꢀC(2)
N(11)ꢀMo(1)ꢀN(1)ꢀO(1)
N(31)ꢀMo(1)ꢀS(1)ꢀC(1)
N(31)ꢀMo(1)ꢀS(2)ꢀC(2)
N(31)ꢀMo(1)ꢀN(1)ꢀO(1)
S(1)ꢀMo(1)ꢀS(2)ꢀC(2)
ꢃ52.9(3)
49.2(3)
ꢃ52.0(2)
53.5(2)
ꢃ50.5(2)
50.5(2)
ꢃ149.6(3)
ꢃ162.0(17)
178.0(100)
104.0(4)
146.6(3)
ꢃ99.0(7)
125.9(3)
ꢃ127.8(3)
59.0(9)
ꢃ146.8(2)
ꢃ161.0(3)
125.0(5)
132.8(12)
150.9(2)
ꢃ153.0(5)
129.0(2)
ꢃ124.0(2)
50.0(7)
ꢃ146.62(19)
ꢃ138.3
138.60(10)
138.3(14)
146.6
ꢃ138.60(10)
128.24(19)
ꢃ128.2
0.00(6)
ꢃ37.4
42.02(3)
ꢃ42.02(3)
37.41(17)
142.6
ꢃ35.5(3)
80.0(7)
ꢃ34.60(18)
28.0(5)
S(1)ꢀMo(1)ꢀN(1)ꢀO(1)
S(2)ꢀMo(1)ꢀN(1)ꢀO(1)
S(2)ꢀMo(1)ꢀS(1)ꢀC(1)
ꢃ5.0(7)
35.3(3)
ꢃ56.0(5)
35.0(2)
Mo(1)ꢀS(1)ꢀS(2)ꢀC(2)
138.4(3)
29.0(7)
138.8(2)
29.7(4)
Mo(1)ꢀS(2)ꢀC(2)ꢀC(1)
Mo(1)ꢀS(1)ꢀC(1)ꢀC(2)
SꢀS bite distance:
Mo distance from N2S2 plane
C36-centroid of C1and C2
Fold angle (u)
31.6
ꢃ31.6
ꢃ31.2(7)
3.192
0.069
ꢃ29.5(5)
3.195
0.071
3.201
0.063
4.198
4.185
4.159
42.0
5.0
41.1
5.6
44.4
5.3
Dihedral angle (between planes: Mo1ꢀN11ꢀN21 and Mo1ꢀS1ꢀS2)
˚
S distances of 2.375 and 2.357 A in complex 7 do
˚
S2) of 86.14(10) A in 1, 87.26(14) A in 2, and 87.63(13)
˚
A in 3 are the most acute in all of the structurally
˚
Moꢀ
/
not significantly vary from those in 1 through 3 despite
the significant change in the nature of the sulfur donor
ligand (1,1?-dithiaferrocenyl-S,S?) in 7 [55]. Table 2
shows that there are no significant changes observed in
characterized mononuclear Group VI transition metalꢂ
/
nitrosyl complexes containing at least two sulfur donor
ligands2.
Moꢀ
ligands, however, significant differences are observed in
S1
/
S distances between chelate rings and non-chelated
The dihedral angle (8d) (Table 2) between the planes
Mo1ꢀ
/
N11ꢀ
/
N21 and Mo1ꢀ
/
S1ꢀ
/
S2 groups the ene-1,2-
1748) from
1758
bond angles of S atoms with axial ligands (N1ꢀ
/
Moꢀ
/
dithiolate compounds 1ꢂ
the other complexes in Chart 1. The value of 8dꢁ
/
3 are distinct (8dꢂ
/
or S2). Bond angles N1ꢀ
/
Moꢀ
/
X (Xꢁ
/
centroid of S1 and
/
for 1 and 174.78 for 3 is significantly larger than 161.98
and 162.28 in corresponding oxo-Mo complexes. This is
2
˚
This angle has the largest value of 161.862 A in (1,2-bis(2-
˚
NO bond (1.818(6) A in 1 and
due to the longer Moꢀ
/
mercaptophenylthio)ethane) ꢂ
molybdenum(II) complex [58].
/
nitroso ꢂ
/
trimethylphosphine ꢂ
/
˚
1.774(6) A in 3) whereas a lone pair interaction of

H.K. Joshi et al. / Inorganica Chimica Acta 337 (2002) 275ꢂ
/
286
283
Fig. 6. The orbital splitting diagram for the molybdenum t2g orbitals
of the [Mo(NO)]3ꢀ and [MoO]3ꢀ cores [62,63].
contrast to what is observed in the oxo-Mo systems
where it ranges from 6.98 in (Tp*)MoO(bdtCl2) to 29.58
in (Tp*)MoO(qdt) [4,35,36,52,53]. The (bdt) ring struc-
ture itself is essentially planar in all of the complexes. As
mentioned earlier, compounds 1ꢂ
angles not withstanding their acute ONꢀ
which are ꢀ
/
3 have large fold
MoꢀS angles,
S angles in the
/
/
Fig. 4. Compound (Tp*)Mo(NO)(bdtCl2) (3) in Pnma space group,
orientation along c axis in a unit cell.
/
148 smaller than the Oꢀ
/
Moꢀ
/
analogous oxo-Mo compounds [4,35,52,53].
In summary, the molecular structures of 1, 2 and 3
show that remote substituents on ene-1,2-dithiolate
ligand do not significantly alter the structural para-
meters of the inner coordination sphere of the Mo
center. However, a change of axial ligand (E) from oxo
to nitrosyl induces significant changes in the fold angle
strongly bonded terminal oxo atom (Moꢀ
/
Oꢁ1.678(4)
/
˚
A
˚
in (Tp*)MoO(bdt) and 1.679(3)
(Tp*)MoO(bdtCl2)) draws the Mo atom out of N2S2
(N11ꢀN21ꢀS1ꢀS2) plane. This is also indicated by
relatively smaller Mo distances from N2S2 plane (Table
A
in
/
/
/
˚
˚
3) in the reported complexes (0.069 A in 1 and 0.063 A
in 3) compared with their oxo analogues (0.264 and
and the Eꢀ
large fold angle in nitrosylꢂ
smaller EꢀMoꢀX angle is intriguing. A CSD search for
the transition metal complexes containing an ene-1,2-
dithiolate chelate showed a range (0ꢂ528) of fold angles
[59]. A majority of these complexes have planar (uꢁ
/
Moꢀ
/
X angle (Xꢁ
/
centroid of S1, S2). The
˚
0.258 A, respectively) [4,35,36,52,53].
The ene-1,2-dithiolate fragment does not show sig-
/Mo complexes despite their
/
/
nificant structural differences with remote substitution
˚
C bond length of 1.742 A
/
as indicated by the average Sꢀ
/
˚
˚
/
in 1, 1.743 A in 2 and 1.743 A in 3 and the Cꢁ
/C bond
˚
˚
length of 1.406 A in 1, 1.413 A in 2 and 1.431 A in 3. The
˚
0.08) ene-1,2-dithiolate rings but some of them are
folded by as much as 5283 [59,61]. The fold angle range
in the structures of Group VI transition metal ene-
most significant structural difference between
(Tp*)MoE(Sꢀ
angle (d) formed between the ene-1,2-dithiolate (Sꢀ
CꢀS) least-squares plane and the SꢀMoꢀS plane along
the line of intersection containing the SÁ Á ÁS atoms (see
Fig. 2(B)). This angle in 1 is 137.98, and thus the SꢀCꢁ
CꢀS plane is folded up toward the terminal nitrosyl
group by uꢁ1808ꢂdꢁ42.18. This fold angle is 41.18 in
/
S) systems (where, Eꢁ/NO, O) is the
dithiolene complexes is 0ꢂ
value of the fold angle observed in the complexes 1ꢂ
reported here.
/
44.48 (Fig. 5) with the largest
/
Cꢁ
/
/
3
/
/
/
The geometric structure perturbations in terms of the
fold angle has implications with respect to the significant
differences between the electronic structures of
/
/
/
/
/
/
(Tp*)MoE(Sꢀ
/
S) (EꢁNO, O). In these compounds the
/
2 and 44.48 in 3 and thus increases slightly with respect
to the electron withdrawing nature of the remote
substituent on ene-dithiolate. The fold angle is in
strong covalent bonding of the {MNO}4 group leads to
an energetically isolated LUMO which is a nonbonding
metal d-orbital (dxy) (Fig. 6). The short Moꢀ
/
O bond in
(Tp*)MoO(Sꢀ
/
S) complexes, on the other hand, dom-
inates the splitting of t2g orbitals (strong s and p donor
oxo-ligand) [62,63]. The electronic configuration of the
oxo-Mo(V) systems is (dxy)1(dxzdyz)0 and the nitrosylꢂ
/
Mo(II) is (dxzdyz)4(dxy)0. The dxy
LMo(NO)(SC6H5)2 (where Lꢁ
h5-C6H5, Tp*(8)),
{MNO}4 complexes with filled dxz and dyz orbitals, is
maximized by a ONꢀMoꢀSꢀC torsion angle near 0 and
1808 Fig. 2(A), [20,21]. The torsion angle ONꢀMoꢀSꢀ
ꢂ
/
Sp overlap in
/
/
/
/
/
/
/C
3
The most folded ene-1,2-dithiolate ring has been observed in the
disordered structure of a uranium complex where uꢁ76.218 [60].
Fig. 5. The distribution of fold angles (u) of ene-1,2-dithiolates in
/
Group VI transition metalꢂene-1,2-dithiolate complexes.
/

284
H.K. Joshi et al. / Inorganica Chimica Acta 337 (2002) 275ꢂ
/
286
0
with (dxy
)
electronic configuration have the most
folded ene-1,2-dithiolate (1ꢂ
/
3: uꢁ
/
41.1ꢂ44.48) in related
/
Group VI complexes. We postulate that the fold angle
should decrease as the complexes 1ꢂ
/
3 are reduced to
1
(dxy
)
and the ene-dithiolate should become close to
planar (0#
metalloceneꢂ
(u) close to 08 in the 18 electron d2 complexes; upon
oxidation this angle increases to uꢁ45ꢂ508 in the 16
electron d0 complexes [24,25,61,64,65]. The electronic
origin of the fold angles in compounds 1ꢂ3 and their
/
08) on further reduction to (dxy)2. The
/dithiolene complexes show a fold angle
/
/
/
oxo-analogues is a current active research area in our
laboratory [29,37].
3.3. Photoelectron spectroscopy
A stack plot of He I gas phase valence PES of 1, 2 and
3 in the region 5.00ꢂ15.00 eV is displayed in Fig. 7. The
/
region from 8.00 to 15 eV is primarily due to the ligand
ionizations (Tp*, benzene ring, nitrosyl group). The
broad Tp* ionization centered about 9 eV is also
observed in analogous compounds with terminal oxo
and sulfido groups [43]. In compound 3, chlorine lone
pair-based ionization appearing at 10.76 (0.02) eV is
easily assigned based on its reduced intensity in the He
II excitation source (spectrum not shown). The ioniza-
tions appearing at lower energy than 8.00 eV, assigned
to the sulfur and the molybdenum based molecular
orbitals, are broader in the nitrosyl complexes (1, 2 and
3) than their oxo-Mo analogues [43]. The first ionization
energies of 6.95 (0.02) eV for 2, 6.97(0.02) eV for 1, and
7.06 (0.02) eV for 3 (Table 4) suggest that electron
withdrawing substituents on the ene-1,2-dithiolate sta-
bilize the HOMO. However, this effect is less than that
observed for the oxo-Mo counterparts, where the energy
range is 0.8 eV [37]. The details of the PES studies and
DFT calculations which probe bonding interactions in
Fig. 7. He I PES of (Tp*)Mo(NO)(Sꢀ
/
S) complexes ((Sꢀ
/
S)ꢁbdt(1),
/
tdt(2) and bdtCl2(3).
in the above two LMo(NO)(SC6H5)2 compounds are 12
and ꢃ1748 in the former and ꢃ16 and ꢃ1688 in the
/
/
/
latter and indicate that the electronic structure of L has
little influence on the overall stereochemistry of the
complex [20,21].
We believe that the fold angle in compounds 1ꢂ3 has
/
an electronic origin that may be attributed to the
interaction of sulfur lone pairs (Spz orbitals) with the
metal d-orbitals. The folding of the ene-1,2-dithiolate
minimizes the interaction of the filled Spz orbitals with
the filled metal dxz and dyz orbitals and favors the
bonding interaction between the Spz orbitals and the
empty metal dxy orbital Fig. 2(B). It has been observed
that the electronic occupation of dxy orbital has
significant effect on the fold angle. The complexes
(Tp*)MoE(Sꢀ
/
S) (EꢁNO, O) complexes will be dis-
/
cussed in more detail elsewhere [29,37].
Table 4
First ionization energies in He I gas phase photnelectron spectra for (Tp*)Mo(E)(SꢀS) systems
Complex
Ionization energy (eV, 90.02 eV)
a
b
EꢁNO
EꢁO
Band 1
Band 2
Band 3
Band 1
Band 2
(Tp*)Mo(E)(tdt) (1)
(Tp*)Mo(E)(bdt) (2)
(Tp*)Mo(E)(bdtCl2) (3)
6.90
6.97
7.06
7.56
7.64
7.78
7.82
7.83
8.43
6.35
7.04
7.26
ꢀ7.50
7.53
7.64
a
Ref. [29,43].
Ref. [35,37,43].
b

H.K. Joshi et al. / Inorganica Chimica Acta 337 (2002) 275ꢂ
/
286
285
[7] J. Miller, A. Epstein, W. Reiff, Chem. Rev. 88 (1988) 201.
[8] T. Yonemura, K. Okamoto, T. Ama, H. Kawaguchi, T. Yasui, J.
Inorg. Biochem. 67 (1997) 11.
4. Conclusions
The synthesis, structural and physical characteriza-
[9] T. Ueno, Y. Suzuki, S. Fujii, A. Vanin, T. Yoshimura, Biochem.
Pharmacol. 63 (2002) 485.
tion of three (Tp*)Mo(NO)(Sꢀ
provided an opportunity to investigate the geometric
and electronic structure differences of (Tp*)MoE(SꢀS)
(where EꢁO, NO) systems as a function of axial
/
S) compounds have
[10] G. Karupiah, Q. Xie, R. Buller, C. Nathan, C. Duarte, J.
MacMicking, Science 261 (1993) 1445.
/
[11] P. Coppens, I. Novozhilova, A. Kovalevsky, Chem. Rev. 102
(2002) 861.
/
ligation and remote substituent effects on the ene-1,2-
dithiolate ligand. The most significant structural differ-
ence is the large fold angle of ene-1,2-dithiolate along Sꢀ
S axis in the nitrosylꢂMo compounds. It has been
postulated earlier that the variation in the fold angle of
pyranopterin-ene-1,2-dithiolate may control the electro-
nic structure of the Mo center of enzymes and could
play a regulatory role in their catalysis [35,36]. The
[12] J.H. Enemark, R.D. Feltham, Coord. Chem. Rev. 13 (1974) 339.
[13] B.L. Westcott, J.H. Enemark, in: E.I. Solomon, A.B.P. Lever
(Eds.), Inorganic Electronic Structure and Spectroscopy; Volume
II: Applications and Case Studies, Wiley, New York, 1999, pp.
/
/
403ꢂ450.
/
[14] S. McWhinnie, C. Jones, J. McCleverty, D. Collison, F. Mabbs,
Polyhedron 11 (1992) 2639.
[15] S. McWhinnie, J. Thomas, T. Hamor, C. Jones, J. McCleverty, D.
Collison, F. Mabbs, C. Harding, L. Yellowlees, M. Hutchings,
Inorg. Chem. 35 (1996) 760.
reduction potential of these (Tp*)Mo(NO)(Sꢀ
/
S) com-
[16] N. Alobaidi, C. Jones, J. McCleverty, Polyhedron 8 (1989) 371.
[17] B. Coe, C. Jones, J. McCleverty, D. Bloor, P. Kolinsky, R. Jones,
J. Chem. Soc., Chem. Commun. (19) (1989) 1485.
pounds is sensitive to peripheral substitution of the
ligand, whereas the first ionization energy is not. This
diversity is due to the different orbitals involved in each
of these processes and supports the electronic structure
[18] Cambridge Structural Database, Cambridge University, Cam-
bridge, UK (accessed May, 2002).
[19] N. Alobaidi, C. Jones, J. McCleverty, Polyhedron 8 (1989) 1033.
[20] M.T. Ashby, J.H. Enemark, J. Am. Chem. Soc. 108 (1986) 730.
[21] S.A. Roberts, J.H. Enemark, Acta Crystallogr., C 45 (1989) 1292.
[22] M. Kamata, K. Hirotsu, T. Higuchi, K. Tatsumi, R. Hoffmann,
T. Yoshida, S. Otsuka, J. Am. Chem. Soc. 103 (1981) 5772.
[23] M. Kamata, T. Yoshida, S. Otsuka, K. Hirotsu, T. Higuchi, M.
Kido, K. Tatsumi, R. Hoffmann, Organometallics 1 (1982) 227.
[24] N. Avarvari, E. Faulques, M. Fourmigue, Inorg. Chem. 40 (2001)
2570.
origin behind the fold angles in Moꢂnitrosyls containing
/
an ene-1,2-dithiolate. A more detailed computational
analysis of the effect of fold angle on the electronic
structures using density functional method is in progress
[29,37].
Acknowledgements
[25] M. Fourmigue, Coord. Chem. Rev. 178ꢂ180 (1998) 823.
/
[26] D.M. Giolando, K. Kirshbaum, Synthesis 5 (1992) 451.
[27] R. Codd, A. Astashkin, A. Pacheco, A. Raitsimring, J. Enemark,
J. Biol. Inorg. Chem. 7 (2002) 338.
Mass spectra were recorded at the University of
Arizona Mass Spectrometry Facility; NMR studies
were carried out at the NMR Facility University of
Arizona, PES studies were carried out at the Center for
Gas-Phase Electron Spectroscopy, University of Arizo-
na under the direction of Dr. Nadine Gruhn. We thank
Dr. Michael Bruck and Dr. Carina Grittini for the
collection of X-ray data on (Tp*)Mo(NO)(bdt) and
(Tp*)Mo(NO)(tdt), Anne McElhaney for electrochemi-
cal data and Dr. J. Jon, A. Cooney for reading the
manuscript. Support by the National Institutes of
Health (Grant GM-37773 to J.H.E.) is gratefully
acknowledged.
[28] J.H. Enemark, M.M. Cosper, in: A. Sigel, H. Sigel (Eds.), Metal
Ions in Biological Systems, Marcel Dekker, New York, 2002, pp.
621ꢂ653.
/
[29] F.E. Inscore, H.K. Joshi, N.E. Gruhn, M.L. Kirk, J.H. Enemark,
manuscript in preparation.
[30] R. Hille, Chem. Rev. 96 (1996) 2757.
[31] R. Hille, J. Biol. Inorg. Chem. 1 (1996) 397.
[32] R. Hille, Essays Biochem. 34 (1999) 125.
[33] F.E. Inscore, R. McNaughton, B. Westcott, M.E. Helton, R.
Jones, I.K. Dhawan, J.H. Enemark, M.L. Kirk, Inorg. Chem. 38
(1999) 1401.
[34] A. Rompel, R.M. Cinco, J.H. Robblee, M.J. Latimer, K.L.
McFarlane, J. Huang, M.A. Walters, V.K. Yachandra, J. Synchr.
Radiat. 8 (2001) 1006.
[35] F.E. Inscore, H.K. Joshi, A.E. McElhaney, J.H. Enemark, Inorg.
Chim. Acta 331 (2002) 246.
References
[36] F.E. Inscore, N. Rubie, H.K. Joshi, M.L. Kirk, J.H. Enemark,
submitted for publication.
[37] H.K. Joshi, F.E. Inscore, Gruhn N.E., J.H. Enemark, manuscript
in preparation.
[1] T.W. Hayton, P. Legzdins, W.B. Sharp, Chem. Rev. 102 (2002)
935.
[38] W. Armarego, D. Perrin, Purification of Laboratory Chemicals,
4th ed., Pergamon Press, New York, 1997, p. 512.
[39] J.A. McCleverty, D. Seddon, N.A. Bailey, N.J. Walker, J. Chem.
[2] G.B. Richter-Addo, P. Legzdins, Metal Nitrosyls, Oxford Uni-
versity Press, Oxford, 1992.
[3] N. Alobaidi, S. Salam, P. Beer, C. Bush, T. Hamor, F. McQuillan,
C. Jones, J. McCleverty, Inorg. Chem. 31 (1992) 263.
[4] I.K. Dhawan, Dissertation, The University of Arizona, Tucson,
AZ, 1995, p. 244.
Soc., Dalton Trans. 10 (1976) 898ꢂ908.
/
[40] S. Reynolds, C. Smith, C. Jones, J. McCleverty, Inorg. Synth. 23
(1985) 4.
[41] D.T. Cromer, J. Waber, Int. Tables X-Ray Crystallogr. 4 (1974)
[5] M. Green, S. Marder, M. Thompson, J. Bandy, D. Bloor, P.
Kolinsky, R. Jones, Nature 330 (1987) 360.
[6] H. Stumpf, L. Ouahab, Y. Pei, D. Grandjean, O. Kahn, Science
261 (1993) 447.
71.
[42] D.T. Cromer, J.A. Wabers, Int. Tables X-Ray Crystallogr. 4
(1974) 148.

286
H.K. Joshi et al. / Inorganica Chimica Acta 337 (2002) 275ꢂ286
/
[43] B. Westcott, N. Gruhn, J. Enemark, J. Am. Chem. Soc. 120
(1998) 3382.
[54] J. Huang, R. Ostrander, A. Rheingold, M. Walters, Inorg. Chem.
34 (1995) 1090.
[44] D.L. Lichtenberger, G.E. Kellogg, J.G. Kristofzski, D. Page, S.
Turner, G. Klinger, J. Lorenzen, Rev. Sci. Instrum. 57 (1986)
2366.
[55] R. Sidebotham, P. Beer, T. Hamor, C. Jones, J. McCleverty, J.
Organomet. Chem. 371 (1989) C31.
[56] S.C. Davies, D.L. Hughes, R.L. Richards, J.R. Sanders, Dalton 5
[45] A.S. Drane, J.A. McCleverty, Polyhedron 2 (1983) 53.
[46] H. Hinton, H. Chen, T. Hamor, C. Jones, F. McQuillan, M.
Tolley, Inorg. Chem. 37 (1998) 2933.
(2000) 719ꢂ725.
/
[57] D. Sellmann, J. Keller, M. Moll, C. Campana, M. Haase, Inorg.
Chim. Acta 141 (1988) 243.
[47] A.E. McElhaney, F.E. Inscore, J.T. Schirilin, J.H. Enemark,
submitted for publication.
[58] D. Sellmann, H. Kremitzl, F. Knoch, Inorg. Chim. Acta 225
(1994) 163.
[59] Please see supplementary data.
[48] N. Alobaidi, M. Chaudhury, D. Clague, C. Jones, J. Pearson, J.
McCleverty, S. Salam, J. Chem. Soc., Dalton Trans. 7 (1987)
1733.
[60] T. Arliguie, M. Fourmigue, M. Ephritikhine, Organometallics 19
(2000) 109.
[49] H. Adams, N. Bailey, A. Drane, J. McCleverty, Polyhedron 2
(1983) 465.
[61] F. Guyon, C. Lenoir, M. Fourmigue, J. Larsen, J. Amaudrut,
Bull. Soc. Chim. Fr. 131 (1994) 217.
[50] J. McCleverty, A. Drane, N. Bailey, J. Smith, J. Chem. Soc.,
Dalton Trans. 1 (1983) 91.
[62] B.E. Bursten, R.H. Cayton, Organometallics 6 (1987) 2004.
[63] B.L. Westcott, J.H. Enemark, Inorg. Chem. 36 (1997) 5404.
[64] I.V. Jourdain, M. Fourmigue, F. Guyon, J. Amaudrut, Organo-
metallics 18 (1999) 1834.
[51] J. Huang, R. Ostrander, A. Rheingold, Y. Leung, M. Walters, J.
Am. Chem. Soc. 116 (1994) 6769.
[52] I.K. Dhawan, A. Pacheco, J.H. Enemark, J. Am. Chem. Soc. 116
(1994) 7911.
[53] I.K. Dhawan, J.H. Enemark, Inorg. Chem. 35 (1996) 4873.
[65] M. Fourmigue, C. Lenoir, C. Coulon, F. Guyon, J. Amaudrut,
Inorg. Chem. 34 (1995) 4979.